Manufacture of semiconductor single crystals having a diameter of 450 mm or more by the Czochralski (CZ) method needs a single-crystal manufacturing apparatus to have a large opening in its hot zone or the apparatus itself so as to allow each semiconductor single crystal being manufactured to pass through the interior of the apparatus. As the area of this opening is increased, an exposed area of polycrystalline silicon raw material contained in a quartz crucible to a chamber is increased. This increase facilitates heat transfer due to radiation between the polycrystalline silicon raw material and the chamber when the polycrystalline silicon raw material is melted, thereby making it difficult to increase the temperature of the polycrystalline silicon raw material.
Accordingly, a high power heater is needed to melt the polycrystalline silicon raw material. This imposes a great burden on the quartz crucible containing the polycrystalline silicon raw material, thereby heavily damaging the quartz crucible. A long operation consequently becomes impossible. There is a need for a manufacturing apparatus that can melt the polycrystalline silicon raw material with a low heater power.
When large diameter crystals, particularly crystals having a large diameter of 450 mm or more and a long length are manufactured, a dash necking method cannot be used, because a neck portion in the dash necking method has a thin width of about 2 to 3 mm and is hence too weak to hold a heavy crystal. Manufacture of crystals by a dislocation-free seeding method is accordingly needed in which a crystal diameter can be optionally selected during its growth after the seeding. In this dislocation-free seeding method, the minimum crystal diameter after the seeding is previously determined such that this diameter allows a single crystal having a prescribed weight to be held; the growth of this single crystal is started after a seed crystal with a sharp end is slowly dipped into a melt of polycrystalline silicon raw material such that the diameter of the grown crystal is within the range of the minimum diameter.
The dislocation-free seeding method, however, literally needs dislocation-free seeding. It is accordingly necessary to prevent the single crystal from generating dislocation after the seeding due to dislocation generated in the seed crystal by a thermal shock caused by difference in temperature between the seed crystal and the melt of polycrystalline silicon raw material. The seed crystal needs to be heated to reduce this difference in temperature between the seed crystal and the melt before the seeding process. A method of heating the seed crystal that is usually used is to move the seed crystal to right above the melt and heat the seed crystal by radiant heat from the melt surface.
However, an increase in diameter of the opening through which the single crystal passes during its growth is accompanied with the enlargement of the diameter of a silicon single crystal to be manufactured, and facilitates heat transfer due to radiation between a seed chuck holding the seed crystal and a chamber, thereby making it impossible to sufficiently heat the seed crystal in the process of heating the seed crystal before the seeding. A success rate of the dislocation-free seeding is thereby greatly reduced.